Place the diced chicken in a medium bowl and toss with 1 teaspoon salt, 1 teaspoon onion powder, 1 teaspoon garlic powder, 1/2 teaspoon black pepper, and 1/2 teaspoon dried thyme until evenly coated.
Heat a large skillet over medium heat and melt 3 tablespoons butter. Add the seasoned chicken and cook, turning occasionally, until cooked through and registering 165°F; about 6-8 minutes depending on size. Remove the chicken to a plate and set aside.
Add 1 tablespoon butter to the skillet, then add the diced onion and diced red bell pepper and cook 1–2 minutes until beginning to brown. Add the garlic and cook 1 more minute, stirring.
Pour in the 2 cups low-sodium chicken stock and bring to a boil. Add the broccoli florets, cover the skillet, and cook 2 minutes to slightly soften.
Remove the lid and push the vegetables to the sides of the pan. Let the stock simmer until reduced by about half, about 5 minutes.
Stir in the remaining 1 tablespoon butter, return the cooked chicken and any accumulated juices to the skillet, and toss to coat and rewarm. Taste and add additional salt and pepper as desired, then serve hot.